In electrodeposition plants, particularly in plants for the electrorefining, electroplating or electrowinning of non-ferrous metals, production and the quality of the metal produced depend, among other things, on the density and distribution of electric current in the electrodes of each elementary cell of the electrolysers.
In particular, one of the main factors that can affect the efficiency and quality of production is related to the occurrence of irregularities in the electric current distribution in the electrodes, due to situations of overcurrent or anomalous current reductions. For example, in plants for the electrowinning of metals, the cathodes of each elementary cell have to be removed from their seats periodically for the metal collection operations. These frequent movements may result in imperfect electrical contacts after the electrodes have been repositioned in their seats, causing irregularities in the distribution of the supply current in the electrodes, and consequently reducing production quality and efficiency. It must also be borne in mind that the deposition of metal on the electrode sometimes takes place in a non-uniform way, resulting in anomalies in the electric current distribution. An example of this phenomenon can be seen in the case of copper electrowinning, where greater metal deposition is frequently found in the lower and/or lateral portion of the cathode. Another situation which may give rise to large irregularities in current distribution is related to the growth of dendritic formations on the electrodes, as found, in particular, in the processes of electrowinning of copper, cadmium or zinc. When these dendritic formations come into contact with the facing electrode, they may create electrical short circuit situations which can seriously compromise metal production, by drawing supply current away from the other electrodes of the electrolyser, possibly causing irreparable damage to the electrodes involved in the short circuit.
In order to control the situations of irregular current distribution described above, current alarm and monitoring devices are sometimes used in metal electrorefining, electroplating and electrowinning plants. These devices are typically positioned on the electrode structure (on the electrode hanger bar, for example) or on the corresponding power supply busbar; alternatively, they may be located near the electrochemical cells, by being suspended or placed adjacent to them. In the latter case, the accurate and reliable identification of the current flowing through the electrode is greatly complicated by the fact that signals of different origin reach the device simultaneously, the analysis of these signals requiring the use of complex mathematical models. This complexity has the practical effect of making it difficult to detect in a reliable manner the small current signal variations due to irregularities in the current distribution.
On the other hand, if the current alarm and monitoring device is positioned on the cathode or anode structure, the power supply to the device has critical elements which have an impact on its practical use. The presence of power supply wires directly on the electrode structure is highly undesirable, owing to the corrosive environment in which they are located, which may cause rapid deterioration of the wires (possibly even creating naked flames, with obvious consequences for the safety of the plant). The presence of wires may also impede the metal collection operations, or in any case the access to the electrodes, and therefore constitutes a hazard or at least an inconvenience for the plant operators. The use of batteries or other energy storage means, with a limited service life, overcomes the problems of power supply caused by the presence of wires, but is not a satisfactory solution, because of the implications in terms of maintenance: the operations of checking and replacing the batteries of the device in an electrowinning plant for the purpose of ensuring their correct and reliable operation would have to be performed frequently on a large number of electrodes and in unhealthy environmental conditions, causing discomfort for the plant personnel.
It is therefore desirable to provide a solution for the aforementioned problems, for example in the form of electrode structures for non-ferrous metal electrorefining, electroplating or electrowinning plants having an electric current alarm and detection device which requires few maintenance operations, has a guaranteed service life of several years, and provides simple and reliable electric current signal detection.
It should also be noted that, according to the operating parameters of the plant, the occurrence of situations of overcurrent or other irregularities in electric current distribution is frequently associated with low signal variations which may be difficult to discriminate from the variations due to signal noise. It is therefore desirable to provide a current signal acquisition and processing system such that its reliability and efficiency are maximized, to be used in combination with electric current alarm and monitoring devices capable of detecting the current signal directly on the electrode structure.